Process and circuitry for generating current pulses for electrolytic metal deposition

ABSTRACT

The invention relates to a method of generating short, cyclically repeating, unipolar or bipolar pulse currents I G , I E  for electroplating, and to a circuit arrangement for electroplating with which pulse currents I G , I E  can be generated. Electroplating methods of this type are referred to as pulse-plating methods. According to the invention, the secondary winding 6 of a current transformer 1 is connected in series into the electroplating direct current circuit 5, consisting of a bath direct current source 2 and a bath which is contained in an electroplating cell and which is represented by resistor R B . The primary winding 7 of the transformer has a larger number of turns than the secondary winding. The primary winding is controlled with pulses of high voltage and with relatively low current. The high pulse current on the secondary side temporarily compensates in pulses the electroplating direct current. This compensation can be a multiple of the electroplating current, such that deplating pulses with high amplitude are produced. The capacitor 10 guides the compensating current through charging and discharging. Through the invention, the necessity of using in pulse-plating the known electronic high current switches, which work uneconomically because of the great current conduction losses, is avoided.

SPECIFICATION

The invention relates to a method for generating short, cyclicallyrepeating, current pulses with great current intensity and with greatedge steepness. In addition, it relates to a circuit arrangement forelectrolytic metal deposition, especially for carrying out this method.The method finds application in electrolytic metal deposition,preferably in the vertical or horizontal electroplating of printedcircuit boards. This type of electroplating is referred to aspulse-plating.

It is known that the electrolytic deposition of metals can be influencedwith the aid of pulse-like currents. This affects the chemical andphysical properties of the layers deposited. It also affects, however,the even deposition of the layer thickness of the metals on the surfaceof the workpiece to be treated, the so-called dispersion. The followingparameters of the pulsating electroplating current influence thesequalities:

Pulse frequency

Pulse times

Pause times

Pulse amplitude

Pulse rise time

Pulse fall time

Pulse polarity (electroplating, deplating).

In publication DE 27 39 427 A1, electroplating with a pulsating bathcurrent is described. The unipolar pulses here have a width of 0.1millisecond maximum. The pulse time, the pause time and the pulseamplitude are all variable. Semiconductor switches, here in the form oftransistors, serve to generate these pulses. What is disadvantageousabout this is that, through the use of switching transistors, themaximum applicable pulsating bath current is technically andeconomically limited. The upper limit lies at approximately 100 amperes.

The process described in the publication DE 40 05 346 A1 avoids thisdisadvantage. Here thyristors which can be switched off are used asquick switching elements (GTO: Gate turn-off thyristor) to generate thecurrent pulses. Technically available GTOs are suitable for currents ofup to 1,000 amperes and more.

In both cases, the technical outlay has to be reflected, i.e. to bedoubled, if bipolar pulses are used. In publication GB-A 2 214 520,which is likewise concerned with pulse plating, a second bath currentsource is avoided in one form of embodiment by using mechanical,electromechanical or semi-conductor switches to reverse the polarity ofthe direct current voltage fed in. The necessary high current switchesare disadvantageous however. Moreover this system is inflexible sincethe method must proceed in both polarities with the same currentamplitude, for, with short high current pulses, the amplitude cannot bereadjusted quickly enough in the bath current sources which areavailable in practice. Thus, in a further form of embodiment in thispublication, two bath current sources are also used which can beadjusted independently of one another. These bath current sources areconnected via a change-over switch with the work-piece located in theelectrolytic cell and the electrode. Since in printed circuit boardelectroplating, for reasons of the precision required (constancy of thelayer thickness), it is necessary to use individually adjustable bathdirect current sources for the front side of the printed board and therear side of same, there is a doubling of the outlay which is necessaryfor realizing this method according to this form of embodiment, to fourbath current sources altogether.

In addition to this high technical outlay, especially for the respectivesecond bath current source per printed circuit board side, theelectronic high current switches cause great energy losses. On eachelectronic switch, when it is switched on, a voltage drop occurs on theinner non-linear resistor when the current flows. This is true for allkinds of semi-conductor elements in the same way, however with varyingsizes of voltage drop. With increasing current, this drop in voltage,also called saturation voltage or forward voltage U_(F), becomesgreater. With the currents usually used in electroplating technology,e.g. at 1,000 amperes, the forward voltage U_(F) on diodes andtransistors amounts to approximately one volt and on thyristorsapproximately two volts. The power loss P_(V) at each of thesesemi-conductor elements is calculated according to the formula P_(V)=U_(F) ×I_(G), I_(G) being the electroplating current. Where I_(G)=1,000A, the dissipated energy P_(V) reaches 1,000 watt to 2,000 watt.The heat produced additionally by the electronic switches has to becarried away by cooling. In the actual bath current source, a power lossoccurs likewise of at least the same magnitude, which is unavoidable.These losses are not to be included in the further considerations. Onlythe power losses which have to be additionally applied to pulsegeneration are taken into consideration.

An electroplating system consists of a plurality of electroplatingcells. They are fed with large bath currents. As an example, ahorizontal system for depositing copper on printed circuit boards fromacid electrolytes will be looked at. The application of the pulsetechnology improves the amount of the copper deposition in the fineholes of the printed boards quite substantially. What has provedparticularly effective is changing the polarity of the pulses in cycles.With cathodic polarity of the article to be treated, for example currentpulses with ten milliseconds pulse width are used. This pulse can befollowed by an anodic pulse with a width of one millisecond. Inpulse-like cathodic electroplating, preferably a current density ischosen which is greater than, or the same as, the current density whichis used with this electrolyte during direct current electroplating.During the short anodic current pulses, a deplating process with asubstantially higher current density takes place than during thecathodic pulse phase. Advantageous here is approximately the factor 4 ofthe anodic to the cathodic pulse phase.

The printed boards are electroplated on both sides, i.e. on their frontand their rear sides with separate bath current supplies. As an examplefive electrolytic baths of a horizontal electroplating system are lookedat. They have per side, for example, five bath current supply units eachwith 1,000 amperes of nominal current, i.e. 10 bath current supplyappliances with 10,000 amperes in total. The bath voltage forelectroplating with acid copper electrolytes is from 1 to 3 volts and isdependent on the density of the current. Because of the high currents,the energy balance for the circuit proposed in the publication DE 40 05346 A1 is looked at as an example (FIG. 7). A positive pulse generatedwith this circuit arrangement as an electroplating pulse with a width oft=10 milliseconds and a negative pulse as a deplating pulse with aconsiderably higher amplitude with a width of t=1 milliseconds, underliethe following consideration. Inaccuracies caused by low edge steepnessesare here disregarded. Thus for the span of 10 milliseconds, thesemi-conductor elements 6, 9, 5 in the circuit arrangement shown in FIG.7 carry the full electroplating current. The power loss of theseswitching elements amounts, per bath current supply with the forwardvoltages U_(F) quoted above, to (2 volts+1 volt+2 volt)×1,000amperes=5,000 watts. For the span of one millisecond, the semi-conductorelements 7 and 8, corresponding to the task set, then carry four timesthe current. This power loss amounts to P_(V) =(2 volts+2 volts)×4,000amperes=16,000 watts. The average high current switch power loss of acycle lasting 11 milliseconds is thus approximately 6,000 watts. Withten bath current supplies this amounts to a power loss of 60 kW(kilowatts). To determine the degree of efficiency, this output must becompared with the output which is converted directly at the electrolyticbath for electroplating and for deplating. The bath voltages are, forthis purpose, assumed to be for acid copper baths with 2 volts forelectroplating and with 7 volts for deplating. Thus the average value ofthe overall bath output for pulse electroplating amounts toapproximately 4.5 kW (for 10 milliseconds, 2 volts×1,000 amperes and for1 millisecond, 7 volts×4,000 amperes). With the losses calculated aboveamounting to 6 kW, only the efficiency of the high current switches,related to the overall bath output, is clearly below 50%.

An electroplating system equipped with electronic high current switchesin this way works completely uneconomically. Moreover the technicaloutlay for the electronic switches and their cooling is very high. Theresult of this is that pulse current appliances of this kind are alsolarge in volume which works against placing them in spatial proximity tothe electrolytic cell. This spatial proximity is however necessary inorder to achieve the required edge steepness of the bath current in thecell at the electrodes. Long electrical conductors work with theirparasitic inductances against any quick rise in current.

In comparison to the electronic switches, electro-mechanical switcheshave a much lower voltage fall when they are in the switched state.Switches or protection devices are, however, completely unsuitable forthe required high pulse frequency of 100 Hertz. For the describedtechnical reasons, the known method of pulsed electroplating isrestricted to special applications and by preference to low pulsecurrents as far as electroplating is concerned.

Thus the problem underlying the present invention is to find a methodand a circuit arrangement with which it is possible to generate short,cyclically repeating, unipolar or bipolar high currents forelectroplating without the disadvantages mentioned occurring, especiallywithout said currents being generated with a considerable power loss.Moreover, the necessary electronic circuit for this method should alsobe realized at a favorable price.

The purpose is fulfilled by the present invention.

The invention consists in the fact that there is coupled into anelectroplating direct current circuit, called a high current circuit forshort, comprising a bath direct current source, electrical conductorsand an electrolytic cell with the electroplating article and anode in aninductive manner by means of a suitable component, for example a currenttransformer, a pulse current with such polarity that the bath directcurrent is compensated or over-compensated. The component is connectedin series with the electrolytic electroplating cell. For example, tothis end, the secondary winding of the current transformer with a lownumber of turns is connected to the bath direct current circuit inseries in such a way that the bath direct current flows through it. Inthe primary winding, the current transformer has a high number of turns,such that the pulses feeding it in accordance with the turns ratio canhave a low current with high voltage. The induced pulsed low secondaryvoltage drives the high compensation current. A capacitor, which isconnected in parallel to the bath direct current source, serves to closethe current circuit for the pulse compensation current.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in detail with the aid of FIGS. 1-6. Theseshow:

FIGS. 1a-1e unipolar and bipolar electroplating current paths, such asare usually used in practice;

FIGS. 2a and 2b circuit arrangement for feeding the compensation currentinto the high current circuit; FIG. 2a is applicable duringelectroplating and FIG. 2b during deplating;

FIG. 3 a schematic representation of the current diagram for the bathcurrent using the circuit arrangement shown in FIG. 2;

FIG. 4a voltage curves in the high current circuit, taking into accountthe rise and fall times;

FIG. 4b an electrical wiring diagram with potentials entered;

FIG. 5 a possible control circuit for the current transformer;

FIG. 6 an overall view of the circuit arrangement to be used forelectroplating printed circuit boards;

In FIG. 7 a traditional circuit arrangement, described in DE 40 05 346A1, is shown.

In the figures a bath current, indicated as positive, should apply forthe electrolytic metallization, i.e. the article being treated is ofnegative polarity in relation to the anode. A bath current indicated asnegative should apply for the electrolytic deplating. In this case, thearticle to be treated is of positive polarity in relation to the anode.

The diagram in FIG. 1a applies to electroplating with direct current. InFIG. 1b the bath current is interrupted for a short time. It remains,however, unipolar i.e. the polarity of the current direction is notreversed. The pulse times lie by preference in the order of magnitude of0.1 milliseconds up to seconds. The pause times are correspondinglyshorter. FIG. 1c shows a unipolar pulse current with differentamplitudes. FIG. 1d shows a bipolar current, i.e. a pulse current whichis briefly reversed in polarity with a long electroplating time and witha short deplating time. The deplating amplitude here amounts to amultiple of the metallizing amplitude. However, altogether, with anelectroplating time of e.g. 10 milliseconds and with a deplating time of1 millisecond, there is a clear excess of the amount of charge neededfor electroplating as opposed to that needed for deplating. This pulseform is particularly suitable for electroplating on both sides printedcircuit boards with fine holes. In FIG. 1e, a double pulse form is shownwhich can be achieved with the method according to the invention.Unipolar pulses here alternate with bipolar pulses.

The electroplating cell represents for the electroplating current anohmic load as a good approximation. With a bath current supply accordingto FIG. 1b, bath current and bath voltage are therefore in phase. Thelow parasitic inductances of the electrical conductors to theelectrolytic cell and back to the current source can be disregarded.Pulse currents contain on the other hand alternating currents. Withincreasing edge steepness of the pulses, the proportion of the highfrequencies of the alternating currents becomes greater. Steep pulseedges have a short pulse rise and fall time. The line inductancesrepresent inductive resistors for these alternating currents. They delaythe pulse edges. However these effects are not considered below. Theyare independent of the type of pulse generation and therefore always thesame if special measures are not taken. The simplest measures consist inusing electrical lines with very low ohmic and inductive resistances. Inthe figures, in order to simplify the drawing, the electroplatingcurrent is always represented as, or assumed to be, in phase with thevoltage.

FIGS. 2a and 2b show the feeding in, according to the invention, of thecompensating pulse current by means of the current transformer 1. Thebath direct current source 2 is connected via electrical lines 3 withthe electrolytic bath, which is here represented as the bath resistorR_(B) with the reference number 4. The secondary winding 6 of thecurrent transformer 1 is connected into this high current circuit 5 inseries with the electrolytic bath. The primary side 7 of the transformeris fed by the pulse electronic unit 8. The pulse electronic unit 8 issupplied with energy via the main supply 9. The current and voltagepaths for the pulses according to FIG. 1d correspond in principle alsoto the pulse forms of the other diagrams in FIG. 1. They differ only inthe momentary size of the compensating current. For this reason thevoltages or currents belonging to FIG. 1d are indicated in the followingfigures and considered.

FIG. 2a shows the state of operation during the electroplating. As anexample, potentials are indicated in brackets. The capacitor C ischarged to the voltage U_(C) ≈U_(GR). The voltage U_(TS) at the currenttransformer 1 amounts to 0 volts. Thus, apart from voltage drops at theline resistors and at the resistor of the secondary winding 6, therectifier voltage U_(GR) is present at the bath resistor R_(B) andcauses the electroplating current I_(G). This temporary statecorresponds to electroplating with direct current. In the high currentcircuit 5, no switches are needed according to the invention.

FIG. 2b shows the state of operation during deplating. The potentialscan no longer be considered static. Therefore in FIG. 2b, the potentialsfor the end in time of the deplating pulse are shown in brackets. Thestarting point is provided by the potentials of FIG. 2a. The power pulseelectronic unit 8 feeds the primary winding 7 of the current transformer1 with a current which alters its amplitude in time. The current flowtime corresponds to the time of the flow of the compensating current inthe main current circuit 5. The primary voltage U_(TP) at thetransformer is such that, corresponding to the number of turns in thetransformer winding a transformer pulse voltage U_(TS) is achievedsecondarily, which is in a position to drive the required compensatingcurrent I_(K). Here, the capacitor C with the time constant T=R_(B) ×C,proceeding from the voltage U_(C) ≈U_(GR), is further charged with thevoltage U_(TS). The charging current is the compensating current I_(K)and at the same time the deplating current I_(E). With a large capacityof the capacitor C, the rise in voltage in the short time of the chargecurrent flow can be kept low. Instead of the capacitor C, an storagecell or storage battery can also be used in principle. The bath directcurrent source 2, consisting of a rectifier bridge circuit, switchesitself off automatically for the period of the deplating, becausethrough the charge, the voltage becomes U_(C) >U_(GR). Without anyadditional switching elements being used, the direct current source 2,during the period of time in which the bath current I_(GR) is fed by theinduced voltage U_(TS) into the current circuit, therefore feeds nocurrent into the current circuit automatically. After the currentcompensation, the bath current is, however, supplied again from thedirect current source. To avoid any short reverse flow in theswitching-off moment with slow rectifier elements in the bath directcurrent source 2, a choke 11 can be inserted into the high currentcircuit 5. The energy for deplating is applied via the currenttransformer 1. The high, yet short in time, deplating current I_(E) inthe secondary winding 6 is fed in primarily. The current is reduced withthe current transformer reduction ratio u.

If this transformer has a reduction ratio of e.g. 100:1, for acompensating current I_(K) of 4,000 amperes only approximately 4 ampereare to be fed in primarily. For the secondary voltage U_(TS) =10 volt inthis example approximately 1,000 volts are necessary primarily. Thepower pulse electronic unit is thus to be dimensioned for high voltageand for relatively low pulse currents. Semi-conductor elements which arefavourable in price are available for this. Thus, no high current switchis necessary even for the high deplating current in the main currentcircuit 5.

The power loss incurred for pulse generation is very low in comparisonwith known methods. The calculation of the dominating losses alreadyshows the difference: in the power pulse electronic unit for generatingpulse currents on the primary side, amongst other things consisting ofan electronic switch with a forward voltage U_(F) =2 volts, the switchpower loss amounts to P=40 amperes×2 volts×(approximately) 10% currentflow time≈8 volts. In the same way, 8 watts are necessary for thereversed transformer current flow to the saturation of the transformer.With ten bath current supplies there is thus a power loss ofapproximately 160 watts altogether. For the comparison of the totalswitch losses of the circuit according to the invention with the lossesof the known circuits, the current transformer losses must be includedwith the circuit according to the invention. If a very good coupling ofthe transformer is used, for example with a strip-wound cut toroidalcore and with highly permeable thin metal sheets, a transformerefficiency of η=90% can be counted on. Thus these losses amount with acompensating current of 4,000 amperes and a voltage of 7 volts withapproximately 10% current flow time to altogether approximately 560watts. This produces for ten bath current supplies, according to theinvention, a total power loss for generating the pulse electroplatingcurrent amounting to 160 watts for the switches and 5,600 watts for thecurrent transformers. This sum includes approximately 6 kW for thedominating losses. In the example calculated above, according to thestate of the art where 10 bath currents supplies were used, thisamounted on the other hand to approximately 60 kW.

The technical outlay for carrying out the method according to theinvention is likewise substantially lower than when traditional circuitarrangements are used. only passive components are loaded with the highelectroplating currents and with the even higher deplating currents.This substantially increases the reliability of the pulse current supplyequipment. Electroplating systems equipped in this way therefore have aclearly higher availability. This is achieved, moreover, withsubstantially lower investment outlay. At the same time, the continuingenergy consumption is lower. On account of the lower technical outlay,the volume of pulse devices of this kind is small, with the result thatit makes it easier to realise them in proximity to the bath. The lineinductances of the main current circuit are therefore also reduced to aminimum.

In FIG. 3 the path of the pulse current is represented diagrammaticallyat the bath resistor R_(B) (electroplating cell 20). On account of theohmic resistor R_(B), the bath current and bath voltage are here inphase. At the point in time t₁, the flow of the compensating currentbegins. The size and direction are determined by the instantaneousvoltages U_(C) and U_(TS). At the point of time t₂, the compensatingcurrent flow finishes. The following electroplating current I_(G) isdetermined by the rectifier voltage U_(GR), in each case in connectionwith the bath resistor R_(B).

The time course of the voltages is represented more accurately in thediagrams of the FIGS. 4a and 4b. The electroplating current I_(G) ispractically in phase with the electroplating voltage U_(G). I_(G) istherefore not indicated because it has the same path. At the point oftime t=0, the rectifier voltage U_(GR), the capacitor voltage U_(C) and,moreover, also the electroplating voltage U_(G) are approximately thesame. The voltage U_(TS) amounts at this point in time to 0 volts. Atthe point in time t₁, the rise of the voltage pulse U_(TS1) begins atthe secondary winding 6 of the current transformer 1. The voltageU_(TS1) is of such polarity that the electroplating voltage U_(G1)becomes negative, with the result that it is possible to deplate. U_(G)is formed from the sum of the instantaneous voltages U_(C) and U_(TS).The voltage U_(TS) is poled at the capacitor C in the direction of theexisting charge. The capacitor C therefore begins to charge itself againto the voltage U_(TS) with the time constant T=R_(B) ×C. At the point oftime t₂, the drop in the voltage pulse U_(TS1) begins. Because of thefinal inductivity of the current transformer secondary circuit, thefalling voltage pulse does not end at the zero line. Through voltageinduction, a voltage U_(TS2) with reverse polarity occurs. This is nowadded to the capacitor voltage U_(C). At the bath resistor R_(B), abrief excessive rise in voltage U_(G2) occurs. The capacitor C begins todischarge itself with the time constants T=R_(B) ×C, it being at leastpartially or even completely discharged. At the time point t₃, thevoltage U_(TS) therefore amounts to 0 volts. The bath direct currentsource U_(GR) takes over again the feeding of the bath resistor R_(B),such that U_(G) ≈U_(GR). The voltages U_(GR), U_(C) and U_(G) are thenapproximately the same size again. The brief excessive rise of voltageat the bath resistor R_(B) is undesired for electroplating purposes. Inpractice this peak and the additional peaks, differently from what isshown here, are clearly rounded. A recovery diode, parallel to thesecondary winding or parallel to an additional winding on the core ofthe current transformer, effects if necessary a further weakening of theincrease in voltage at the bath resistor R_(B). On the other hand, thelow excessive voltage then is present longer. There will be no furtherdiscussion of these systems of wiring inductances, nor likewise of theconstruction of the current transformer which is to be constructed as apulse transformer. Pulses are to be fed on the primary side into thetransformer in such a way that magnetic saturation of the transformeriron is avoided. For desaturation, there is after each current pulsesufficient time available in the pulse pauses to feed in a current withreverse polarity. To this end, an additional winding can be attached tothe transformer core. FIG. 5 shows an example of the primary sidetriggering of the current transformer 1. An auxiliary source 12 issupported by a charging capacitor 13 with the capacity C. An electronicswitch 14, here an IGBT (Isolated Gate Bipolar Transistor) is triggeredby voltage pulses 15. In the switched state of the electronic switch 14,a primary current flows into the partial winding I of the primarywinding 7 of the current transformer, and to simplify the circuit adesaturation current in the partial winding II. When the switch is notconnected, only a desaturation current flows in the partial winding II.To reduce the outlay, a possible additional electronic switch for thiscurrent is dispensed with. The number of turns in the partial windings Iand II as well as the protective resistor 17, via which a current of lowmagnitude flows permanently, are so adapted to one another that nosaturation of the transformer iron occurs. The current diagram 18 inFIG. 5 shows diagrammatically the primary current I_(TP).

FIG. 6 shows the application of the pulse current units 19 in anelectroplating bath 20 with goods to be electroplated arrangedvertically, for which bath two bath direct current sources 2 for therear side and the front side of the flat article to be electroplated,for instance a printed circuit board, are used. Each side of the printedboard 21 is separately supplied with electroplating current from one ofthese current sources 2. Opposite each side of the printed board ananode 22 is arranged. During the short deplating pulse, these anodeswork as cathodes in relation to the article to be treated which is thenpoled anodically. Both pulse current units can work either inasynchronous or synchronous manner with one another. To electroplate theholes of printed boards, it is advantageous if the pulse sequences ofthe same frequency of both pulse current units are synchronised and ifat the same time there is phase displacement of the pulses. The phasedisplacement must be such that, during the electroplating phase on theone printed board side, the deplating pulse occurs on the other side andthe other way round. In this case, the dispersion of the metal, i.e. theelectroplating of the holes, is improved. The pulse sequences of thesame frequency can, however, where there is separate electrolytictreatment of the front and the rear side of the article to be treated,also run asynchronously towards one another.

The invention is suitable for all pulse electroplating methods. It canbe used in electroplating systems, dipping systems and feed-throughsystems, working vertically or horizontally. In the feed-throughsystems, plate-shaped goods to be electroplated are held in a horizontalor vertical position during the treatment. The times and amplitudesmentioned in this specification can be altered within wide ranges inpractical applications.

    ______________________________________                                        Terms used in the specification                                               ______________________________________                                        U.sub.G      Electroplating voltage                                           U.sub.GR     Rectifier voltage                                                U.sub.C      Capacitor voltage                                                U.sub.TP     Primary transformer pulse voltage                                U.sub.TS     Secondary transformer pulse voltage                              U.sub.F      Forward voltage                                                  I.sub.G      Electroplating current                                           I.sub.E      Deplating current                                                I.sub.K      Compensating current                                             P.sub.V      Power loss                                                       u            Current transformer reduction ratio                              ______________________________________                                    

    ______________________________________                                        List of reference numbers                                                     ______________________________________                                        1         Current transformer                                                 2         Bath direct current source                                          3         Electrical conductors                                               4         Bath resistor R.sub.B                                               5         High current circuit                                                6         Secondary winding of the current transformer                        7         Primary winding of the current transformer                          8         Power pulse electronic unit                                         9         Mains supply                                                        10        Capacitor with the capacity C                                       11        Choke                                                               12        Auxiliary voltage source                                            13        Charging capacitor with the capacity C.sub.L                        14        Electronic switch                                                   15        Voltage pulses                                                      16        Voltage diagram                                                     17        Protective resistor                                                 18        Current diagram                                                     19        Pulse current unit                                                  20        Electroplating cell                                                 21        Goods to be treated                                                 22        Anode                                                               ______________________________________                                    

What is claimed is:
 1. Method for generating cyclically repeating,unipolar or bipolar pulse currents I_(G), I_(E) for electroplating,characterized in that there is coupled in an inductive manner into anelectroplating direct current circuit (5), formed from a direct currentsource (2) and an electroplating cell (20) with a bath which exhibitsresistance R_(B), by means of a transformer (1) connected in series withthe electroplating cell (20), a compensating pulse current I_(K) of suchpolarity that the bath current supplied from the direct current source(2) is compensated or overcompensated to form the unipolar or bipolarpulse currents, there being a capacitor (10) connected in parallel tothe direct current source (2) and in close spatial proximity to theelectroplating cell (20).
 2. Method according to claim 1 characterizedin that the capacitor (10) is partially discharged during periods oftime in which the bath current is not compensated or overcompensated. 3.Method according to claim 1, characterized in that, in order to generateunipolar current pulses, the amplitude of the compensating pulse currentI_(K) is set to be equal to or less than the amplitude of the bathcurrent supplied from the direct current source (2).
 4. Method accordingto claim 1, characterized in that, in order to generate bipolar currentpulses, the amplitude of the compensating pulse current I_(K) is set tobe greater than the level of the bath current supplied from the directcurrent source (2).
 5. Method according to claim 1, characterized inthat pulse current for metallization I_(G) and pulse current fordeplating I_(E) are applied and the amplitude of the pulse current fordeplating I_(E) is set to be higher than the amplitude of the pulsecurrent for metallization I_(G) and that the pulse width of the currentI_(E) is set to be shorter than the pulse width of the current I_(G). 6.Method according to claim 1, characterized in that a separateelectrolytic supply for each of the front side and rear side of anarticle being electroplated with pulse current is provided, and thesame-frequency pulse sequences of the two sides are adjusted to besynchronous.
 7. Method according to claim 6, characterized in that aconstant phase displacement between the pulse currents on the front andrear side of the article being electroplated is set in such a way thatdeplating of said article does not occur on both sides at the same time.8. Method according to claim 1, characterized in that a toroidal currenttransformer is used as the transformer (1) connected in series with theelectroplating cell.
 9. Circuit arrangement for electroplating withwhich cyclically repeating, unipolar or bipolar pulse current I_(G),I_(E) is generated, comprising an electroplating direct current circuit(5) formed from a direct current source (2) and an electroplating cell(20), means (8) for generating a pulse current, and a transformer (1)connected in series with the electroplating cell (20) for inductivelycoupling a compensating pulse current I_(K) from the pulse currentgenerating means (8) into the electroplating direct current circuit (5),wherein compensating pulse current I_(K) is of such polarity that thebath current supplied from the direct current source (2) is compensatedor overcompensated to form the unipolar or bipolar pulse currents, andfurther comprising a capacitor (10) connected in parallel to the directcurrent source (2) and in close spatial proximity to the electroplatingcell (20).
 10. Circuit arrangement according to claim 9 whereintransformer (1) has a primary winding (7) and a secondary winding (6),the secondary winding being connected in series with the direct currentsource (2) and the primary winding having a larger number of turns thanthe secondary winding.